1. Field of the Invention
The present invention generally relates to a shared active pixel sensor (APS). In particular, the present invention is directed to a shared active pixel sensor so that a single multi-share pixel unit can serve as multiple pixels.
2. Description of the Prior Art
A photodiode is a semiconductor device for use as an image sensor. Basically speaking, to make an image sensor more sensitive, it is a good idea for a photodiode to occupy an area as large as possible so regions other than the photodiode region in each pixel should be minimized. For the sake of saving more pixel area, pixels are always designed to share read out circuits with other neighboring pixels.
In terms of the number of sharing pixels, there are various sharing pixels, for example a 2-share or a 4-share pixel. Generally speaking, a reset transistor or a source follower is the first candidacy. Otherwise, it is only one option available to reduce the STI (shallow trench isolation) area or the floating diffusion area to achieve a high conversion gain or high sensing area.
Accordingly, another novel pixel structure is still needed for minimizing the pixel area.